1. Field of the Invention
The application relates to a method utilized in a wireless communication system and a communication device thereof, and more particularly, to a method of handling buffer status report in a wireless communication system and a related communication device.
2. Description of the Prior Art
Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system established upon the 3G mobile telecommunication system, supports only packet-switched transmission, and tends to implement both Medium Access Control (MAC) layer and Radio Link Control (RLC) layer in one single communication site, such as in Node B (NB) alone rather than in NB and RNC (Radio Network Controller) respectively, so that the system structure becomes simple.
In LTE, MAC provides transmission services via a plurality of logic channels. To manage uplink resources, when a user equipment (UE) performs uplink (UL) transmission, the network can divide or map logical channels of the UE into at most four groups based on priorities, types, QoS and so on. The 3rd Generation Partnership Project, 3GPP, introduces a buffer status reporting (BSR) procedure, which is used to provide enhanced NB (eNB) with information about an amount of data in UL buffer (hereafter called a buffer size) of a logical channel group in the UE. Note that, the buffer status report is realized by reporting an index in a buffer size table (BST) for indicating the buffer size of the logical channel group. Beside, the UE can report at most four buffer size table indexes in the buffer status report.
Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced system is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced system targets faster switching between power states, improves performance at the cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), uplink multiple input multiple output (MIMO), etc.
For bandwidth extension, carrier aggregation is introduced to the LTE-Advanced system for extension to wider bandwidth, where two or more component carriers are aggregated, for supporting wider transmission bandwidths (for example up to 100 MHz) and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, where the UE can establish multiple links corresponding to the multiple component carriers for simultaneously receiving and/or transmitting.
In the LTE system, a buffer size table is defined for the UE supporting a single component carrier. The index numbers of the buffer size table are represented by 6 bits (e.g. index=‘0’-‘63’), and each index number indicates a buffer size value. For example, the index=‘0’ indicates buffer size value is 0 byte (e.g. BS=0), the index=‘1’ indicates buffer size value is greater than 0 and is less or equal to 10 bytes (0<BS<=10), and so on. Note that, for the greatest index number (index=‘63’) in the buffer size table, the buffer size value is indicated greater than 150000 bytes (BS>150000). For the UE supporting only one component carrier, the 6-bit buffer size table is sufficient for buffer status report. However, in the LTE-Advanced system, the UE supports multiple component carriers and UL MIMO, and thereby the transmission data rate is extremely enhanced. Thus, the 6-bit buffer size table is not sufficient for representing the buffer size value of a logical channel group in multiple component carriers. Improper indication may cause that the network (e.g. an eNB) allocates insufficient resource to the UE for data transmission.
Considering a scenario, the buffer size value of the logical channel group in the LTE-Advanced system is greatly larger than 150000 byte (e.g. reaching to 3000000 bytes). Based on the 6-bit buffer size table, the UE reports index=‘63’ in the buffer status report. In this situation, resource allocated by the network to the UE for uplink transmission is not enough since the network does not know accurate buffer size value.